Regardless of one's opinion of him, it's pretty hard to say that a former president of the United States is outside the mainstream.

And Ben Shapiro's podcast is currently the 7th most downloaded podcast in the US[1]. That also qualifies as pretty mainstream.

[1] https://www.podcastinsights.com/top-us-podcasts/

Their positions are not mainstream. His positions are not mainstream.

I can say plenty of negative things about all of those people, including the disingenuous ways all of them argue their points. But all mainstream means is that they have a large audience. Which all of them do.

I don't know this Crowder person, but Shapiro and Trump are absolutely mainstream. Enough that I, a guy who's not from the US and has no interest in its domestic politics, can get Shapiro memes.